1. Field of the Invention
The present embodiments relate to a plasma display panel where the display quality is improved by controlling a crystalline grain diameter and the membrane density of a protective layer.
2. Description of the Related Art
A plasma display panel (PDP) is a display device that forms an image by exciting phosphor with vacuum ultraviolet (VUV) rays generated by gas discharge in discharge cells. Since a PDP is capable of realizing a large, high-resolution screen, it is drawing attention as a next-generation thin display device.
PDPs are broadly classified into alternating current (AC) types and direct current (DC) types. AC PDPs are most widely used.
The AC PDP has a basic structure where two electrodes are arranged crossing each other between two substrates that face each other and are filled with a discharge gas and partitioned by barrier ribs. One electrode is coated with a dielectric layer for generating wall charges and the other electrode is disposed opposite thereto and coated with a phosphor layer. On the dielectric layer, a protective layer that is generally composed of MgO is disposed.
The protective layer has sputtering resistance to compensate the affect due to the ion bombardment of the discharge gas while the plasma display panel is discharged. The protective layer is covered on the dielectric layer in the form of a transparent protective thin film having a thickness of 3,000 to 7,000 Å, which protects the dielectric layer from the ion bombardment and lowers the discharge voltage through the secondary emission of electrons.
Since the characteristics of the protective layer are widely varied depending upon the conditions of the heat depositing process and the layer-forming process, it is hard to maintain display quality within a certain level. The protective layer may cause black noise due to an address discharge delay, which is an address miss where light is not emitted in the selected cell. Black noise generally occurs in a boundary between a light-emitting region and a region where no light is emitted, but may occur in a certain region. An address miss occurs at low intensity when there is no address discharge or when a scan discharge is progressed. Accordingly, research for diminishing the address discharge delay time has been done to prevent the black noise and the discharge miss.
Nowadays, the protective layer for the PDP is generally composed of MgO materials, and formed by sputtering, electron beam plating, ion beam assisted deposition (IBAD), chemical vapor deposition (CVD), and sol-gel processes, but the electron beam plating (EB) process is commonly adapted.
The electron beam plating process forms a MgO protective layer and includes the steps of colliding the electron beam accelerated to the electric field and the magnetic field with a MgO depositing material, and heating and evaporating the depositing material. However, the electron beam plating process has the disadvantage that more production devices are installed if mass production is required to be as much as 60 to 70 Å/sec since the deposition speed is prolonged due to the limit of the heat source of the electron spot source. Further, as it is dependent upon only the acceleration energy generated from the potential difference, the acceleration intensity thereof is insufficient and it limits the forming of a dense protective layer.